1. Field of the Invention
The invention refers to a leak detector for detecting at least one gas component in an aspirated gas.
2. Description of the Related Art
For a leak test using helium as the tracer gas, commercial apparatus generally detect the presence of helium by means of a mass spectrometer whose operation requires the generation of a high vacuum. Another detection method uses a membrane selectively permeable to helium, the membrane closing off a cavity in which a pressure sensor is located. Inside the cavity, a pressure is built that corresponds to the partial pressure of helium in the surrounding atmosphere. The membrane usually needs heating. Such a sensor is referred to as a partial pressure sensor in Wise Technology. It is manufactured by INFICON GmbH. Leak detectors with Wise Technology are described in DE 10 2005 021 909 A1 and in DE 10 2005 047 856 A1. Such sensors in the form of mass spectrometers or partial pressure sensors have a high sensitivity, but are susceptible to excessive concentrations of the tracer gas. The detection of helium by means of Wise Technology is limited to a partial pressure of 0.5 mbar. With gross leaks, the sensor must be protected against high concentrations. After a gross contamination, the device is blind for many seconds so that a user cannot continue the leak test. In particular, it is not possible to localize a gross leak site. When the sniffer probe reaches the vicinity of the gross leak, the system switches the sensor to the blind mode for protection. In a similar manner other sensor systems are susceptible to contamination or saturation. Also when a saturation limit is reached, concentration measurements are no longer possible.
Another sensor of the saturable gas-selective sensor type is the mass spectrometer. The mass spectrometer has a very high sensitivity and gas selectivity, but its operation requires a high vacuum, i.e. a very low value of the total pressure at its measuring input. If the total pressure rises above the allowable limit value, the mass spectrometer reaches the saturation range.